...large as possible) compressed file. Like Derelict, Gtkd, Qtd, Vibe, Apache Thrift. I mean not...

...I'm having trouble with some others like GtkD. Also writeln always does it right.

hbox.add would call packStart with the defaults, witch would be packStart(btn, true, true...

Using add(btn) you would probably end up with a stretched button again. :)
    hbox.packStart...

Thank you, Mike. One more question. Can I use hbox.add(btn); instead of hbox...

...gtk.HButtonBox;

class Application : MainWindow
{
    this()
    {
        super("GtkD App");
        setDefaultSize(200, 200);

        HButtonBox hBox = new...

I can't find any tutorials about buttonboxes. Can you write how to use it?

A VBox or A HBox will always expand the Widget in the direction opposite of...

I'm waiting other answers :)

Try playing with an interactive gui tool, such as glade. The fill, expand and size...